The invention relates to a process for operating a burner fed with liquid fuel, in particular a vaporization burner of a heater with an operations control device, such as a motor vehicle heater, in which combustion air and fuel are conveyed to the burner, optionally pulse fed by a feed and metering pump to produce an ignitable combustible mixture.
In air heaters (i.e., heaters in which air is used as a gaseous heat transfer medium) or in water heaters (in which water or another liquid coolant is used as a liquid heat transfer medium), combustion air and fuel are mixed in a burner to produce an ignition-prone combustible mixture that is burned to produce a flame in a combustion chamber. Hot combustion gases result which transfer their heat, by a heat exchanger, to the liquid or gaseous heat transfer medium. To supply fuel to the burner, a metering and feed pump can be used, for example, an electromagnetically controlled reciprocating pump. Such a pump delivers a pulsed fuel stream to the burner. This pulsed fuel stream can be equalized in the area of the burner, such as a vaporizing burner, so that an almost steady fuel feed amount is obtained.
A process for operating a heater is known from German Offenlegungsschrift 38 22 899 in which the heater can be operated in at least two load stages, a partial load stage and a full load stage. With this process, the procedure is such that the burner operation of the heater is always started in the lower or lowest load stage, and then a switching to the respectively next higher or highest load stage follows. In the respective steady state operating ranges, such as partial load and/or full load, fuel is constantly fed to the burner by the appropriate fuel feed and metering pump.
Tests have shown that, especially with vaporization burners in the steady operating states, such as full load or partial load, there is an increased tendency to form coke deposits and toward carbonization of the vaporizing element of the burner which leads to failure of the burner. After such a burner failure, the heater must be serviced, and usually the whole vaporization burner must be replaced. Especially during prolonged steady operating phases of the burner, a clogging of the vaporizing element due to carbonization is to be expected, and the deposits formed in the burner in the course of it can be reduced to an insufficient extent during nonsteady operating phases, such as starting, stopping, switching.
A process for starting and operating a heating burner, in particular for motor vehicle heating, is known from German Patent 31 36 792 in which the stream of combustion air is fed intermittently in the starting phase after a period of being fed continuously, and preferably, the feeding of the fuel is interrupted, during the intermittent feeding of the stream of combustion air, until the burner ignites. By this method, the glow plugs are effectively prevented from becoming cold in the start-up phase, which is especially important when rod glow plugs are used that do not reach the high surface temperatures of coil glow plugs.
A fuel supply arrangement is known from German Offenlegungsshrift 14 51 389 in which the fuel conveyed by a diaphragm pump to the vaporization burner is reduced, since the fuel requirement of vaporization burners requires only a fraction of the amount that is supplied by the diaphragm pump used as a metering and feed pump. To reduce the fuel conveyed by the diaphragm pump, a device is provided that periodically interrupts the liquid stream. With the help of this device, the fuel amount fed to the vaporizing burner is thus throttled, but the fuel amount in the respective operating states of the burner and of the heater is continuously fed to the burner. Thus, the above-described difficulties also arise with this vaporizing burner.